Japanese Patent Application Laid-Open Publication No. 2006-114575 discloses a scheme in which diodes are provided at two different locations in a power module and a gradient of temperature is detected at each of these two locations based on temperature characteristics of each diode to estimate the life of a power semiconductor element. Japanese Patent Application Laid-Open Publication No. 2000-124781 discloses a scheme in which an internal gate resistor is connected between a gate electrode of an IGBT chip and a gate terminal of an IGBT module including the chip to detect the temperature of the IGBT module by using the temperature characteristics of the internal gate resistor.